diff --git a/lib/matplotlib/backends/backend_cairo.py b/lib/matplotlib/backends/backend_cairo.py
index f788937d0f92..274afbee9329 100644
--- a/lib/matplotlib/backends/backend_cairo.py
+++ b/lib/matplotlib/backends/backend_cairo.py
@@ -488,8 +488,8 @@ def _save (self, fo, format, **kwargs):
                         fo.close()
             surface = cairo.SVGSurface (fo, width_in_points, height_in_points)
         else:
-           warnings.warn ("unknown format: %s" % format)
-           return
+            warnings.warn ("unknown format: %s" % format)
+            return
 
         # surface.set_dpi() can be used
         renderer = RendererCairo (self.figure.dpi)